Copper Chunky example + source

[roondar]

Originally Posted by jotd

roondar I like the video, and also the humility you put in that video.

Isn't it possible to "pipeline" the changes and create 1 pixel color with enough colors? say 8 colors? (possibly what I'm saying is stoopid)

Thanks

Actually, the way I get to 4 pixels per colour is using exactly such a trick. You can do 1 pixel Copper Chunky this way, but it'll only be at most 56 pixels wide because of Copper speed limitations

Originally Posted by redblade

Great tutorial, Also thumbs up for mentioning dr dobbs, I love looking at the articles in that and byte magazine, so much code from the golden days

Good on you for giving love to Amanita Muscaria, I haven't eaten those in years, I prefer psilocybin

Thanks! Yeah, Dr. Dobbs and Byte are great stuff.
As for the mushroom, I haven't actually eaten any ever. What happened is that I needed three pictures and after choosing the one of my cat, I wanted to add more colour so I picked one I took at the zoo and one I took in the forest

[chb]

Originally Posted by jotd

I wonder what was used in the "Brian the lion" title screen with Brian letters wobbling all over.

AFAIK it's a variety of the "shear & zoom" rotator without a need for c2p. You can perform a rotation of up to 45° as a shear in x and y and a downscale. Now the x-shear is trivial on the Amiga with a per-line-scroll. The shear in y can be done with the blitter by using two sources, the same image but one shifted 1 in y-direction, and a mask to alternate between those two. That gives you a maximum of 1 pixel shear per 16 pixel (blitter word), so you're restricted to about 3.5° of rotation per pass. I guess zooming can be done either by the scroll register trick or with the blitter (splitting the image in two parts and removing one line). Or you just accept the "pumping" during rotation as a feature of your effect and skip the zoom altogether.

From the above one can see that this trick is only really well suited for slow & continuous rotations, as you cannot rotate by an arbitrary angle without intermediate steps. That usually gives that kind of effect away. IIRC, the rotating skull in WoC/Sanity uses the same technique.

But back on topic, very nice work & documentation, roondar. Thanks for sharing!

But back on topic, really

[alkis]

Nice video and nice tone on the presentation. Big thumbs up.

[defor]

@Roondar: Thank you. Very nice reading. I was experimenting with copper-chunky during my youth years back in '93 or '94. I didn't know about 7bpls trick back then though, so I was combining bitplanes with sprites. Photon's rotozoomer (which you mentioned) does it too? Does it allow him to stop bitplanes fetching sooner so that CPU can access chip-ram?
Btw I'm not sure about this passage in your article:

The display will work as if it has 6 active bitplanes, but Denise will only fetch 4 of them.

Isn't it Agnus which fetches 4 words only but Denise still combines words from all BPLxDAT registers? What I don't like about 7bpls trick is that it really doesn't work on AGA and therefore one either must implement a workaround or be prepared for angry reactions from people having AGA machines only
Also, I remember that eventually coders used interlace copper-chunky technique more often (copper color change every 8 pixels with a 4 pixel mask which is swapped every line and frame) as it allows full-screen. Looks ugly and dark though
My suggestion for your next article: Zooming, or "star-wars scroller" :-) Is it really possible by modyfing bplcon2 along the line only?

[roondar]

Originally Posted by defor

@Roondar: Thank you. Very nice reading. I was experimenting with copper-chunky during my youth years back in '93 or '94. I didn't know about 7bpls trick back then though, so I was combining bitplanes with sprites. Photon's rotozoomer (which you mentioned) does it too? Does it allow him to stop bitplanes fetching sooner so that CPU can access chip-ram?

Photon's version does use Sprites so he needs less bitplane DMA (he only has a small strip of bitplane DMA active). Not sure if he uses 4 BPL or 7 BPL trick though.

Btw I'm not sure about this passage in your article:
Isn't it Agnus which fetches 4 words only but Denise still combines words from all BPLxDAT registers?

You are 100% correct, luckily, I did say it correctly in the video (because I do know this). I'll fix the article when I next get a chance.
Edit: fixed the article, it now correctly refers to Agnus doing the fetching rather than Denise. Thanks for pointing it out

What I don't like about 7bpls trick is that it really doesn't work on AGA and therefore one either must implement a workaround or be prepared for angry reactions from people having AGA machines only

Yup, my program has a separate code path for AGA because 7BPL trick doesn't work there.

Also, I remember that eventually coders used interlace copper-chunky technique more often (copper color change every 8 pixels with a 4 pixel mask which is swapped every line and frame) as it allows full-screen. Looks ugly and dark though
My suggestion for your next article: Zooming, or "star-wars scroller" :-) Is it really possible by modyfing bplcon2 along the line only?

I never liked the interlaced Copper chunky mode, as you say it's very dark. And thanks for the suggestion, I'll keep it in mind

[Cobe]

Excellent video! Also the ones before were great.

While watching it I got one probably stoopid too idea.
In order to have "higher" vertical resolution, would it be possible to update odd than even lines every other frame. Maybe even having two bitmaps, one with y+1 offset and switching between them... Something like low res interlace. And how would that compare to flat 25fps...

[roondar]

Originally Posted by Cobe

Excellent video! Also the ones before were great.

Thanks

While watching it I got one probably stoopid too idea.
In order to have "higher" vertical resolution, would it be possible to update odd than even lines every other frame. Maybe even having two bitmaps, one with y+1 offset and switching between them... Something like low res interlace. And how would that compare to flat 25fps...

It's not a stupid idea, interlacing to improve resolution is a very old technique and it works really well. It does have drawbacks of course, but all compromises do. It should definitely work, though you may have to be careful about the image you use such that few harsh edges exist between colours (to alleviate the inevitable flicker any form of interlacing introduces).

[buzzybee]

@roondar: Enjoyed each of your videos so much. Thanks a lot for sharing your expertise, and creating code and videos!

Edit: Did read your written feature too. Amazing stuff.

[defor]

I wonder where OCS/ECS copper chunky technique appeared for the very first time.
According to Pouet:
Announce / Lemon (March 1993)
Desert Dream / Kefrens (April 1993)
and much later: Arte / Sanity (November 1993)
My guess is that it all happened under a strong influence of the famous rotozoomer in World of Commodore / Sanity (November 1992), which is not done using copper chunky though.
I know a lot of productions were using copper color modifications + bpl data to squeeze images (usually scroll texts) many years before, but I don't count them as an emulation of chunky buffer per se.
P.S.: I also wonder if all those plasma effects were some kind of precursors.

[DanScott]

Originally Posted by defor

I wonder where OCS/ECS copper chunky technique appeared for the very first time.
According to Pouet:
Announce / Lemon (March 1993)
Desert Dream / Kefrens (April 1993)
and much later: Arte / Sanity (November 1993)
My guess is that it all happened under a strong influence of the famous rotozoomer in World of Commodore / Sanity (November 1992), which is not done using copper chunky though.
I know a lot of productions were using copper color modifications + bpl data to squeeze images (usually scroll texts) many years before, but I don't count them as an emulation of chunky buffer per se.
P.S.: I also wonder it all those plasma effects were some king of precursors.

I think there was some previous to Announce/Lemon.

I remember when it was released, and thinking that it was a nice variation on another one that I'd seen. Will have to have a dig around and see what it was

[guy lateur]

Great stuff! Thanks for creating these!

[LeCaravage]

Always interesting to read Amiga article of yours mate.

[yannc76]

Excellent stuff and big thumbs up for your explanation skills

[Rotschi]

Originally Posted by defor

@Roondar:
Also, I remember that eventually coders used interlace copper-chunky technique more often (copper color change every 8 pixels with a 4 pixel mask which is swapped every line and frame) as it allows full-screen. Looks ugly and dark though

Any examples of demos that made use of this technique? And would this not be prone to flickering?

[Hannibal]

I don't know if anyone released copper-chunky before I released Announce, but I definitely had never seen any before I wrote my version.
The routine from WoC was directly the inspiration - Chaos had snailmailed me that routine as a standalone executable, as a preview for an upcoming demo. I quickly came up with the copper version. I could actually have included it in 3d demo 2 as I had written the effect before its' release. However, I wasn't great at keeping up with new releases, so I didn't see WoC until afterwards, and didn't want to break his trust by releasing my version before him.

[Rotschi]

@Hannibal
That is a nice background story. Thanks for sharing. I would have liked to see Chaos's face :-)
And hadn't you made use of the $102 zoom/shrink trick - though in a very basic version - before Chaos came up with Optimum Fuckup? I seem to remember of having read sth like this.

[Hannibal]

Yeah, 102 zooming in Last Dimension - but not combined with prescaled images, so Chaos' version was much more impressive